1. Field of the Invention
The present invention relates to threaded end protectors for pipes and, more particularly, to a composite end protector having an improved mechanical locking arrangement.
2. Description of the Prior Art
The threaded ends of pipe must be protected from damage during storage and transit. Typically, end protectors have been manufactured from plastic, metal or a combination of the two. The threads of all-metal protectors can damage the pipe threads if misapplied. Further, the metal threads of metal protectors do not prevent the exposure of the pipe threads to moisture and, thus, do not prevent corrosion of the pipe protector. All-plastic end protectors, while eliminating the corrosion and thread damage problems, often become loose during prolonged periods due to expansion and contraction of the threads resulting from exposure to temperature extremes. Further, all-plastic protectors tend to become loose or broken due to deformation caused by impact.
Therefore, workers in the art have developed composite end protectors having a threaded plastic member shielding the threaded pipe end and a metal member shielding and reinforcing the plastic inner member. The metal and plastic members of the protector must be so joined together that they do not become separated from each other when the protector experiences impact during storage or transfer of the pipe, or during any of the numerous applications to or removals from the pipe end encountered during normal use. However, any technique used to join the plastic and metal members must permit economical manufacture and assembly of the protector.
Turk U.S. Pat. No. 4,157,100, which issued on June 5, 1979, discloses a composite threaded end protector having a detent in the metal outer member to mechanically join it to the plastic inner member. The metal detent pierces the plastic member to hold the two members together. The friction forces holding the detent in place can be readily overcome by the blows to the end protector which often occur during transit. The Turk disclosure does not indicate how the metal member is placed on the plastic member. If the detent is formed in the metal member before it is forced onto the plastic member, the metal detent may deform the threaded surface of the protector. When the end protector is placed on the pipe, the deformed threaded surface of the plastic member can strip away the grease which must be applied to the threads of the pipe. If the detent is formed by crimping after the metal member is placed on the plastic member, to maintain the integrity of the plastic threads, the crimping operation complicates the production process and thereby increases production costs.
Waldo et al. U.S. Pat. No. 4,487,228, which issued on Dec. 11, 1984, discloses a cup shaped composite end protector. Holes drilled through the metal outer member receive protrusions molded in the plastic inner member to mechanically join the two. The plastic member may be molded in the metal member to ensure proper alignment of the protrusions with the holes. Alternatively, the members can be formed separately and assembled by placing the metal member over the plastic member. The former method of assembly increases the cost of production and the latter method risks the misalignment of the protrusions and the holes. The plastic protrusions of the misaligned protector deform the threads of the protector, which can cause the grease-stripping problem identified above, and can defeat the seal provided by the threads and cause incomplete coupling between the pipe and protector. Further, the plastic protrusions can be sheared off by a heavy impact resulting in separation of the plastic from the metal member.
Coel et al. U.S. Pat. No. 4,126,338, which issued on Nov. 21, 1978, discloses an arrangement for providing mechanical coupling of plastic shaft sections. Protruding wedges having inwardly sloping ramps on the interior surface of the outer member engage complementary preformed recesses in the outer surface of the inner member. A separately formed keyway and axially extending rib are provided on the shaft sections to ensure alignment of each wedge with its corresponding recess.
It is an object of the present invention to provide a composite threaded end protector which has an improved arrangement for mechanically joining the inner and outer members. It is a further object of the present invention to provide a positive locking attachment which will not become dislodged or worn during transit. It is an object of the present invention to provide an arrangement of mechanical joinder which will facilitate proper alignment. Finally, it is an object of the present invention to provide such an improved end protector which can be produced economically.